Growing cyanobacteria and other photosynthetic microorganisms such as algae also usually requires a large amount of water—they’re grown in ponds or in large clear containers filled with water. Proterro is developing a new bioreactor that does not immerse the cyanobacteria in water. Instead, they’re grown on fabric that’s soaked with water using a drip-feed system. “The organisms don’t need to be submerged, just fed with a trickle of water,” Kasdin says.
The approach is similar to one being developed by Joule Unlimited, except Joule has engineered its organisms to produce fuel directly. Kasdin says Proterro chose a process that the organisms do naturally, which it hopes will make the organisms easier to develop and maintain. She also says that Proterro’s low water bioreactors could also cut costs compared to Joule’s, which immerse the organisms in water.
Proterro, which was founded in 2008 and has raised $5 million in venture funding, is still at an early stage. It’s demonstrated engineered versions of the sugar secreting cyanobacteria, and made prototype bioreactors. But it’s still not clear exactly how high the yields will be, or how much less water will be used than conventional ways of making sugar—or even it if can make sugar cheaper than it can be made from sugarcane.
The fact that the organisms don’t need much water and can secrete the sugar makes the technology attractive, says Jianping Yu, a scientist at the National Renewable Energy Laboratory in Golden, Colorado. What’s more, he says, it’s already been demonstrated that algae and cyanobacteria can produce high yields per acre. But he says the company will face many challenges. The biggest comes from the fact that by secreting sugar, the organisms create an ideal environment for many other organisms. These other organisms could choke out the cyanobacteria, making it necessary to clean the bioreactors frequently and grow new batches of cyanobacteria. That would make the system too expensive.
“Biofuels companies that stick closer to established industrial processes have a better chance of success,” says Mark Bünger, a research director at Lux Research. “The biofuels arena has a lot of challenges, and Proterro is trying to tackle them all at once. It’s a big, bold bet.”